1. Field of the Invention
The present invention relates to a sample introduction apparatus for introducing a sample into an analyzer such as a liquid chromatograph, and more particularly, to a sample introduction apparatus suitable for analysis with pretreatment.
2. Description of the Related Art
Mainly, there are two injection methods in an automatic sample introduction apparatus (also referred to as an autosampler or an autoinjector) for liquid chromatograph. One is a “total volume injection method,” in which a total volume of a sample measured and taken from a sample bottle (vial) is injected, and the other is a “partial injection method,” in which a part of the sample measured and taken from the sample bottle is filled in a sample loop and then injected (for example, refer to “HPLC//LCtalkNo.46, Injection methods of Autosampler (Comparison between Total Volume Injection Method and Partial Injection Method),” Shimadzu Corporation, online, http://www.an.shimadzu.co.jp/support/lib/lctalk/46/46tec.htm, searched on Feb. 21, 2005).
The sample introduction apparatus in the “total volume injection method” uses a sample loop for sample measurement, the sample loop having a needle for sample introduction which is provided at a tip portion thereof, and inserts the needle into the sample bottle. Then, the apparatus sample introduction apparatus suctions the sample into the sample loop by using a syringe, and measures the sample. Subsequently, the apparatus connects the needle to a sample introduction port of the liquid chromatograph, and changes a flow path to feed a mobile phase from the needle to a column through the sample loop. Thus, the apparatus performs sample introduction (for example, refer to JP-A-6-148157).
Since an accuracy of injection amount at the time of the sample injection is high, and there is no loss of the sample due to the total volume injection of the measured sample, the sample introduction apparatus for introducing the sample, such as the liquid chromatograph, often employs the “total volume injection method.”
According to a purpose of analysis or a sample to be analyzed, pretreatment is performed on the sample. This pretreatment is such as concentration control of the sample, addition of an internal standard substance, or formation of a derivative, for example. Such a pretreatment of the sample is performed before the sample bottle is set in the sample introduction apparatus. For example, in an analysis using the liquid chromatograph, there is case where the sample is preliminarily derivatized to a predetermined substance so as to facilitate the detection of the sample. In this case, a prepared sample obtained by mixing the sample and a derivatization reagent to thereby cause a reaction therebetween is introduced into a high-performance liquid chromatograph through the sample introduction apparatus.
In the total volume injection method, cleaning fluid fills inside of the sample loop when inside of the needle is cleaned with the cleaning fluid. Thus, a part of the cleaning fluid may be injected into a flow path of the mobile phase. In a case where the cleaning fluid differs in composition from the mobile phase, it is difficult to clean the inside of the needle sufficiently. Therefore, when the pretreatment is performed on the sample, a sample introduction apparatus in an injection method in which the needle is placed outside the flow path of the mobile phase, that is, the “partial injection method,” is often used. Consequently, in the analysis with the pretreatment of the sample, measurement accuracy deteriorates.
In order to employ the “total volume injection method” in the analysis which requires the pretreatment, an operation can be considered in which the sample, on which the pretreatment is performed, is fed into the sample bottle and then the sample bottle is installed in the sample introduction apparatus. However, this operation is not efficient, since the number of samples is large, the effect of performing the pretreatment varies with time (for example, deterioration of the sample and the mobile phase), and there are losses of the sample and the mobile phase.